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1
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Temperature Dependence of the Viscosity of Isotropic Liquids

100%
Jadżyn J., Czechowski G., Lech T.
Acta Physica Polonica A
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2002
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vol. 101
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issue 4
495-503
EN
Temperature dependence of the shear viscosity measured for isotropic liquids belonging to the three homologous series: 4-(trans-4'-n-alkylcyclohexyl) isothiocyanatobenzenes (C_n H_{2n+1} CyHx Ph NCS; nCHBT, n=0÷12), n-alkylcyanobiphenyls (C_nH_{2n+1} Ph Ph CN; nCB, n=2÷12) and 1,n-alkanediols (HO(CH_2)_nOH; 1,nAD, n=2÷10) were analysed with the use of Arrhenius equation and its two modifications: Vogel-Fulcher and proposed in this paper. The extrapolation of the isothermal viscosity of 1,n-alkanediols (n=2÷10) to n=1 leads to an interesting conclusion concerning the expected viscosity of methanediol, HOCH_2OH, the compound strongly unstable in a pure state.
2
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Viscous Behavior of Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

80%
Jadżyn J., Czechowski G., Laskowski S.
Acta Physica Polonica A
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2006
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vol. 109
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issue 6
723-730
EN
The paper presents results of the shear viscosity measurements performed on diluted binary mixtures of mesogenic solvent n-hexylcyanobiphenyl (C_6H_{13}PhPhC≡N,6CB) and two non-mesogenic admixtures: (i) n-heptylcyanophenyl (C_7H_{15}PhC≡N,7CP), composed of the molecules of the same polarity as the solvent molecules but of a slightly shorter length, and (ii) 4-n-propylcyclohexyl-4'-n-pentylphenyl (C_3H_7CyHxPhC_5H_{11},3CyP5), composed of the non-polar molecules but of a length very close to that of the mesomorphic solvent molecules. The experiment showed that the concentrational depression of the clearing temperature and the temperature extent of the isotropic + nematic (I + N) two-phase region in the mixtures are significantly smaller, i.e. the nematic phase is more thermodynamically stable, when the admixture molecular length is compatible to that of the mesogenic solvent, regardless of the polarity of the admixture molecules. The activation energy for freely flowing mixtures in the isotropic, nematic, and two-phase I + N regions was determined and discussed.
3
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Viscosity Behavior at the Nematic to Smectic A Phase Transition in Freely Flowing Compounds

80%
Jadżyn J., Czechowski G.
Acta Physica Polonica A
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2004
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vol. 105
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issue 5
459-465
EN
The paper shows that the shear viscosity at the nematic to smectic A phase transition in freely flowing n-hexyloxycy$ $anobiphenyl + n-octyloxycyanobiphenyl mixtures (a system exhibiting the reentrant nematic phase) corresponds to the Mięsowicz η_3 viscosity coefficient and its temperature behavior is analogous (but strongly enhanced) to that observed for the η_2 viscosity coefficient at the isotropic to nematic phase transition.
4
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Dielectric, Viscous, and Elastic Properties of Mesogenic 4-n-Hexyloxy-4'-Cyanobiphenyl

80%
Czechowski G., Jadżyn J.
Acta Physica Polonica A
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2001
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vol. 99
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issue 5
579-591
EN
The paper presents the results of measurements of the static and dynamic electric permittivity, the shear viscosity, and the splay and bend elastic constants for 4-n-hexyloxy-4' -cyanobiphenyl (C_6H_{13}O-Ph-Ph-C≡N). On the basis of the static values of the nematic principal permittivities, ε_ǁ (T) and ε_(T), the angle between the dipole moment vector and the long axis of 4-n-hexyloxy-4'-cyanobiphenyl molecule, the apparent dipole moment and the nematic order parameter were determined. From the temperature dependences of the dielectric relaxation time (corresponding to the molecular rotation around the short axis) and the shear viscosity, the strength of the nematic potential and the effective length of 4-n-hexyloxy-4'-cyanobiphenyl molecule (in isotropic phase) were estimated. The K_{11} and K_{33} elastic constants were determined from the voltage dependence of the capacitance of the planar nematic cell with the method proposed by Gruler et al. and Uchida et al.
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